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Phase issues with L and R channels? (Stereo EQ)

zigropolis

Should there ever be a reason to throw the left and right channels of a system out of phase? We have a LA Audio EQ231G-SP and the phase switch can do some interesting things. I am under the impression that you don't want your mains to be out of phase...but the bass response changes drastically when I throw the left side out of phase (it sounds HUGE when out of phase, and balanced when in phase). I think that our subs could be aligned much better...the bass response with both channels in phase is lacking in the center of the room. Has anybody messed around with this before?
September 4, 2008 @10:59pm
DAS

Not sure whether you're asking about L & R being out of phase with each other, or both channels out of phase, but in phase with each other (two very different questions).
I can't think of any good reason to run L & R with phase reversed (with respect to each other). The problems you are describing sound like problems elsewhere in your system. For instance, if the low end in the middle is missing when the EQ is set in phase then I suspect something else is causing L & R to be out of phase with each other to begin with. When you reverse the phase on the EQ you're actually putting the two sides back in phase.
I have been in rooms where the dimensions work out to cause standing waves that cancel near the middle of the room. This is pretty easy to identify because there is always a huge build up of bass near at least one of the edges. Repositioning the PA speakers is the best way to even this out.
Now, if you're asking about putting both L & R out of phase (with everything else), but maintaining the phase with each other then the answer gets a bit more involved. Nevertheless it still isn't something I would do.
I have flipped phase on monitor sends before. This can help with feedback issues and can reduce how much they interfere with the mains.
September 5, 2008 @12:05pm
cmchamp

It sounds to me, from what you're explaining, and the information at hand, that the subs are already out of phase - especially if it's "lacking" in the middle of the room. This may have been done by the installer to keep from creating a "power alley" in the center of the room where the LF frequencies would sum (add together) quite a bit.
C
September 5, 2008 @12:24pm
zigropolis

Thanks for the replies. I have a feeling that you guys are right on about the phase problem coming from elsewhere in the system. The setup is pretty standard...board (main outs) > EQ > crossover > power amps > speakers...I think it might be possible that the guy who installed the speakers wired them out of phase... I have messed with the speaker placements (especially the subs) and have had some success but it doesn't seem to clear the issue up completely so I'll check out the rest of the gear in my signal chain.
September 5, 2008 @07:16pm